Towards strategic control of ticks in the eastern Cape Province of South Africa.

The performance of alphamethrin and flumethrin treated and untreated Bonsmara cows and calves grazing in the thornveld of the Eastern Cape Province was compared over a 2 year period. The economically important tick species occurred seasonally but in insufficient numbers to achieve enzootic stability with respect to babesiosis and anaplasmosis. No differences in live mass were observed for the cows, but the untreated calves were heavier at weaning than the acaricide treated group. Markedly lower numbers of ticks occurred on the calves than on the cows. The implications of the findings are discussed in relation to planning alternative tick control strategies for the region.

An evaluation of strategic and short interval tick control in indigenous exotic and crossbred cattle.

The performance of Nguni, Bonsmara and Hereford oxen which were maintained free of ticks by short interval treatment with acaricide irrespective of tick load (tactical) was compared with similar groups which were treated for tick infestation only when the numbers of adult ticks on the cattle increased to moderately high proportions (strategic). Strategically treated Nguni oxen acquired a strong resistance against ticks and showed weight gains comparable with the tick free Nguni group. Weight gains in the Bonsmara group were higher in the strategically treated group suggesting a possible effect of the acaricide on the tick free group. Strategically treated Hereford oxen acquired heavy tick burdens and performed poorly compared with the tick free group. Practical approaches to strategic tick control under African conditions are discussed.

A survey of small stock tick control practices in the eastern Cape Province of South Africa.

Current small stock tick control practices and producer attitudes towards tick control in the eastern Cape Province of South Africa are discussed. These were ascertained from returns to a questionnaire survey to which 31.2% of farmers polled, responded. In general, producers did not favour an intensive tick control policy for small stock. Angora, mutton and wool farmers had a definite preference for synthetic pyrethroid acaricides, the majority treating either less than 6 times p.a. or between 11-15 times p.a. Most producers changed acaricides because of price. All small stock producers favoured plunge dip application of acaricides while the majority of wool sheep and Angora producers utilized footbath application as a second preference. Mutton producers favoured pour-on and hand spray application as a second choice. Producers who used plunge dip application techniques experienced the highest percentage of confirmed acaricide resistance which is in accordance with application preference. The general incidence of confirmed acaricide resistance, however, was of a low order but highest amongst mutton farmers. An average cost for acaricide treatment of R1.65 per small stock unit p.a. was calculated from data gained in this survey. Only a small number of producers used the available heartwater vaccine. Small stock mortalities experienced by producers per production unit indicated higher mortalities at high acaricidal treatment frequencies. Farmers allowing a small number of ticks to infest their sheep experienced fewer mortalities due to heartwater than those than kept their sheep free of ticks. Angora goat farmers experienced the same, but with higher mortalities, probably due to the apparently high susceptibility of Angora goats to heartwater.

A survey of cattle tick control practices in the eastern Cape Province of South Africa.

Current cattle tick control practices and producer attitudes towards tick control in the eastern Cape Province of South Africa are discussed. These were ascertained from answers to a questionnaire survey to which 31.2% of farmers responded. In general, producers favoured intensive tick control. Beef and dairy farmers had a definite preference for synthetic pyrethroid acaricides, the majority followed a 25 times p.a. treatment frequency and most changed acaricides because of price. Beef producers favoured pour-on application of acaricides while the majority of dairy producers utilized plunge dipping. Producers who used hand spray techniques experienced the highest percentage of confirmed acaricide resistance. A costs of R11.27 for acaricide treatment per bovine per annum was calculated from data gained in this survey. A cost index of 2,496 was calculated by relating acaricide cost to the prevailing price of beef in the region. Only a small number of producers used heartwater, babesiosis and anaplasmosis vaccines. Relative tick borne disease mortality ratios indicated higher heartwater mortalities at high acaricide treatment frequencies. These results are discussed in relation to the tick control regimes practised.

Indigenous and crossbred cattle--a comparison of resistance to ticks and implications for their strategic control in Zimbabwe.

A comparison of the tick resistance of indigenous Mashona and crossbred Afrikander x Sussex oxen following natural tick infestation indicated that significantly more African blue ticks Boophilus decoloratus were found on the crossbred than the indigenous cattle (P < 0.05). The two groups of cattle were exposed to Babesia bigemina and Theileria taurotragi as indicated by high antibody titres on the indirect fluorescent antibody test, but no antibodies could be demonstrated to Anaplasma marginale and T. parva bovis despite the presence of their vectors. Rhipicephalus appendiculatus, Hyalomma truncatum and H. marginatum rufipes showed a seasonal distribution. The implications of the findings in terms of strategic tick control are discussed.

Cross-resistance between instars of the brown ear-tick Rhipicephalus appendiculatus (Acarina: Ixodidae).

Repeated and cross-infestation of rabbits with the larvae, nymphae and adults of Rhipicephalus appendiculatus showed that significant cross-resistance occurs between larvae and nymphae, and nymphae and adults. The implications of these findings in the field situation are discussed.

Specificity and effects of host resistance on the African tick Rhipicephalus zambeziensis (Acarina: Ixodidae).

Repeated infestations of the rabbit with adult Rhipicephalus zambeziensis ticks resulted in a ten-fold reduction in engorgement weight of adult ticks and a significant decline in engorgement weight of nymphs. There was no evidence of cross-resistance against the South African bont tick, Amblyomma hebraeum. Immunization of rabbits with crude extracts of whole-tick protein significantly influenced engorgement weights and oviposition rates of adult R. zambeziensis. Histological studies of tissues from R. zambeziensis adults fed on resistant rabbits showed severe gut damage; this was associated with the binding of host IgG to mid-gut cells.

Acquisition of resistance to the bont tick Amblyomma hebraeum (Acarina: Ixodidae) by goats.

Goats acquired resistance to larvae of Amblyomma hebraeum following three repeated infestations. Resistance was associated with immediate Type I hypersensitivity reactions following intradermal skin tests using crude egg extracts. In a separate experiment, the inoculation of tick-naive goats with extracts of the larvae of A. hebraeum failed to induce observable effects on feeding larvae despite the development of anti-larval antibodies.

Resistance of restrained Bos taurus dairy bull calves to the bont tick Amblyomma hebraeum (Acarina: Ixodidae).

Three infestations of restrained Jersey and Friesland bull calves with adult Amblyomma hebraeum did not affect the rate of engorgement of female ticks and resulted in an insignificant decline in the mean engorgement weight of female ticks recovered from the Friesland group. Repeated infestations significantly affected the egg-laying capacity of engorged female ticks recovered from both groups of hosts. The Friesland calves manifested an enhanced resistance to the larvae and nymphs of Amblyomma hebraeum resulting in prolonged attachment, and a significant decline in engorgement rate of these instars compared with the Jersey group. Skin reaction tests using crude tick extracts yielded antigen-specific hypersensitivity reactions which were not related to resistance to A. hebraeum. Histological changes at the attachment site associated with tick rejection are discussed in relation to host resistance mechanisms.

Immunological responses of the rabbit host to infestation by the brown ear-tick Rhipicephalus appendiculatus (Acarina:Ixodidae).

Rabbits developed resistance to Rhipicephalus appendiculatus instars following repetitive infestations. Rejection was accompanied by elevated IgM and IgG titres. Extracts of salivary gland, mouth-part cement and whole ticks induced a dose-related lymphocyte transformation. Skin-provocation tests with tick extracts elicited an immediate type-I hypersensitivity reaction with a delayed time-course which was influenced by antihistamines. Passive-transfer studies indicated that resistance was partially transferred with serum. A comparative histological study of the attachment sites of larvae on resistant and naive hosts demonstrated the role of eosinophils and macrophages during the initial phase of infestation. Possible rejection mechanisms are discussed in the light of these and other findings.

Helminth and arthropod parasites of Angora goats on irrigated Kikuyu grass pastures in the eastern Cape Province.

Angora goat kids and yearlings grazing irrigated Kikuyu (Pennisetum clandestinum) grass pastures in the eastern Cape Province, became heavily infected with Teladorsagia circumcincta and Trichostrongylus rugatus, leading to high mortality in both age groups. Peak burdens of the former were recorded during March and May, and of the latter during May and June. Larger numbers of the cestode Moniezia expanza, occurred in the kids than in the yearlings. Despite the stress of high helminth burdens, no clinical cases of coccidiosis were seen. Both groups of goats were infested with small numbers of immature stages of the tortoise tick, Amblyomma marmoreum, and the yellow dog tick, Haemaphysalis leachi. Infestation with the biting louse, Damalinia limbata, occurred within 2 d of birth, but never reached very large numbers. Larvae of the nasal botfly, Oestrus ovis, were present only from January to July.

Infestation of cattle by the brown ear tick, Rhipicephalus appendiculatus, does not affect serological responses to foot-and-mouth disease vaccine.

A comparison of the serological responses of tick-free and tick-infested cattle following inoculation with the Botswana SAT 2 foot-and-mouth disease vaccine indicated that infestation by the brown ear tick, Rhipicephalus appendiculatus, did not affect serological responses to the vaccine. This finding implies that infestation by this tick species is unlikely to influence immunity following routine inoculation against foot-and-mouth disease in tick endemic areas.

Immunity of the ox to the brown ear tick Rhipicephalus appendiculatus.

Controlled repeated infestation of Bos taurus and Bos indicus cattle resulted in a decline in the recovery of all R. appendiculatus instars. Resistance to infestation varied between individuals although all individuals manifested severe hypersensitivity at the attachment site, which was reflected in the grooming reflex.

Immune suppression induced by the brown ear tick Rhipicephalus appendiculatus Neumann, 1901.

The brown ear tick Rhipicephalus appendiculatus suppressed in vivo and in vitro immune responses in the rabbit. Humoral responses were suppressed during infestation; however, suppression was transient and was unrelated to previous exposure of hosts to similar tick infestations. Immune suppression was caused by putative lymphocytotoxic factor(s) in tick salivary secretions as evidenced by in vitro lymphocytotoxicity assays. In an identical study of Rhipicephalus zambeziensis, a closely related rhipicephalid, the immune response was not suppressed, indicating that immune suppression is not common to the genus Rhipicephalus.

Lyme disease--a new disease in southern Africa?

Lyme disease is a recently-described zoonotic disease occurring widely in the U.S.A., Europe and Asia. The causative organism, Borrelia burgdorferi, is transmitted predominantly by ticks of the genus Ixodes and infects a wide host range. The infection in humans causes the human disease syndrome erythema chronicum migrans resulting in arthritis, neurological symptoms and/or cardiac abnormalities. Similar clinical signs have been described in domestic animals. The status of Lyme disease in southern Africa is presently unknown but preliminary evidence indicates that the disease may occur in humans in the Republic of South Africa. The abundance of hosts and tick vectors would favour the establishment of the infection in Africa.

Observations on successive infestations of the rabbit host by the ticks Rhipicephalus appendiculatus and R. zambeziensis (Acari: Ixodidae).

Successive infestation of the rabbit host by instars of the brown ear tick Rhipicephalus appendiculatus resulted in a progressive decline in engorgement and egg weights of adult instars and a reduction in percentage recovery of nymphs and larvae. Repetitive infestation with adults and larvae resulted in increased skin hypersensitivity reactions at the attachment site. Successive infestation with R. zambeziensis caused a more significant decline in engorgement and egg weights of adults than for R. appendiculatus. Percentage recoveries of larvae and nymphs were also significantly reduced. A cross-infestation study indicated that R. appendiculatus and R. zambeziensis share antigenic moieties.

Transmission of Theileria parva bovis (Boleni strain) to cattle resistant to the brown ear tick Rhipicephalus appendiculatus (Neumann).

Four crossbred Bos taurus oxen resistant to Rhipicephalus appendiculatus and three tick naive oxen of the same breed, which were all infested with adult R. appendiculatus infected with the Boleni strain of Theileria parva bovis, acquired Theileria infection. All four tick resistant oxen recovered after a mild febrile reaction. Two of the tick naive oxen died while the third recovered after a protracted period. It is suggested that tick resistance in cattle may be an important factor in establishing and maintaining enzootic stability in Theileria endemic areas.

Epidemiology of tick-borne diseases of cattle in Zimbabwe. III. Theileria parva group.

A survey of the occurrence of antibodies to Theileria parva using the IFA test in calves up to one year old at 244 localities in Zimbabwe revealed that the parasite occurred throughout the country although the prevalence of positive serological reactors was generally low. Outbreaks of theileriosis in high rainfall areas in the north, east and west of the country were attributed to Theileria parva bovis transmitted from cattle to cattle by Rhipicephalus appendiculatus. Outbreaks in high and low rainfall areas in the south and west of the country were attributed to Theileria parva lawrencei transmitted from buffalo to cattle by Rhipicephalus zambeziensis or R. appendiculatus. R. appendiculatus was not uniformly distributed in Zimbabwe. It occurred very commonly in foci in the commercial farming areas but was rare in most overgrazed communal farming areas. Outbreaks of disease attributed to T. parva bovis were recorded in some but not all the R. appendiculatus foci. The disease was present in areas infested with R. zambeziensis but it did not cause cattle deaths in these areas.

Epidemiology of tick-borne diseases of cattle in Zimbabwe. II. Anaplasmosis.

A survey on the incidence of antibodies to Anaplasma marginale in one- to three-year-old cattle was carried out in Zimbabwe using the capillary tube agglutination test. Antibodies were detected in all but one of 118 batches of sera collected from different localities throughout the country. There was no clear relationship between the frequency of occurrence of positive serological reactors, which was similar in both commercial and communal farming areas, and the incidence of clinical anaplasmosis. However, the highest numbers of cattle exhibiting positive reactions were generally recorded from the areas that were most heavily tick infested. There was evidence that wild ungulates may serve as reservoirs of infection as antibodies to A. marginale were detected in sera from buffalo (Syncerus caffer) and impala (Aepyceros melampus).